Oxytocin, oxytocin-associated neurophysin, and prostaglandin f2α concentrations in the utero-ovarian vein of pregnant and nonpregnant sheep

S. B. Hooper, W. B. Watkins, G. D. Thorburn

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Oxytocin, oxytocin-associated neurophysin (neurophysin), prostaglandin F2α (PGF2α), and progesterone concentrations were measured in the utero-ovarian vein (UOV) of sheep during the estrous cycle and early pregnancy. On days 13- 16 of the cycle, large pulses of PGF2α, oxytocin, and neurophysin were measured in samples collected at hourly intervals from the UOV draining a corpus luteum (UOV/CL). Most of the PGF2α pulses (96.5%) coincided with a pulse of both oxytocin and neurophysin, whereas only 55.6% of oxytocin pulses coincided with a pulse of PGF2α. Therefore, during luteolysis in sheep, uterine PGF2α release is closely associated with ovarian oxytocin release, and oxytocin release is unlikely to be dependent upon a uterine PGF2α stimulus. During frequent sampling, coincident oxytocin pulses were measured in 1) both UOVs when a CL was present in both ovaries and 2) the jugular vein, carotid artery, and UOV/CL, with a significantly higher oxytocin pulse concentration occurring in jugular venous compared with carotid arterial plasma. Pituitary and luteal release of oxytocin may, therefore, occur simultaneously and be controlled by a circulating factor in sheep. Compared to days 13-16 of the cycle, significantly (P < 0.001) fewer pulses of PGF2α, which were significantly (P < 0.001) smaller in amplitude, were measured in UOV samples collected frequently during early pregnancy. The frequency of oxytocin pulses observed in the UOV/CL of pregnant sheep was not significantly (P < 0.1) different from that observed in cyclic ewes, although most (86.4%) oxytocin pulses occurred in the absence of a PGF2α pulse. In contrast, when a pulse of PGF2α was observed in the UOV/CL of pregnant ewes, it usually coincided with a pulse of oxytocin. The suppression of uterine PGF2α release during early pregnancy is not considered to result from a lack of stimulation by oxytocin.

Original languageEnglish
Pages (from-to)2590-2597
Number of pages8
Issue number6
Publication statusPublished - 1 Jan 1986

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